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New insights into Second soundquench evaluation
Yegor TamashevichDESY/University of Hamburg
TTC2014 Tsukuba
1
Second Sound in liquid Helium
Second Sound is a thermal wave in HeI‐HeIImixture which leads to the phases’ concentrations oscillations
No pressure oscillation ‐> no material transfer
1Russell J. Donnelly ‐ The Observed Properties of Liquid Helium at the Saturated Vapor Pressure
[1]
Could be detected not only by thermometrybut also by Oscillating Superleak Transducer (OST)
Porous membrane
Insert for Vertical Test is equipped with 18 OST
Y.Tamashevich ‐ New insights into Second sound quench evaluation ‐ TTC2014 Tsukuba 2
After processing of signals (t=tsignal‐tquench)point of quench origin should be found
Second Sound test
Signals
The simplest way – to use trilateration.Was used previously for SecondSound tests at DESY2
2Felix Schlander, 2,3Ricarda Laasch
• Not accurate (few cm from surface )
• Uses only OST ‘in sight’• Needs a lot of OST to cover all surface
[3]
[3]
Y.Tamashevich ‐ New insights into Second sound quench evaluation ‐ TTC2014 Tsukuba 3
Ray tracingThe idea is to use 3D simulation to find the shortest paths of second sound from quench point to each OST.
Results of 3D simulations and path calculations are stored in 2D matrices which allows using of these precalculated results during the second sound tests.
Y.Tamashevich ‐ New insights into Second sound quench evaluation ‐ TTC2014 Tsukuba 4
H
r35 r34 r33 r32 r31 r30 r29
r28 r27 r26 r25 r24 r23 r22
r21 r20 r19 r18 r17 r16 r15
r14 r13 r12 r11 r10 r9 r8
r7 r6 r5 r4 r3 r2 r1
0°180° angle
height
0
H
Ray tracing
Distance matrix
Surface coordinates are used to achieve homogeneous coverage of surface along cavities axis
angle
z alingsurface
Y.Tamashevich ‐ New insights into Second sound quench evaluation ‐ TTC2014 Tsukuba 5
Finding the quenchAll signals are fitted by the Second Sound speed (19.9 m/s at 1.8 K)4
Calculated
distance
measured time
Repeat for each point of surface
The region with the lowest fitting errorshows the most probable quench position
Heat propagation effect
4Russell J. Donnelly ‐ The Observed Properties of Liquid Helium at the Saturated Vapor Pressure Y.Tamashevich ‐ New insights into Second sound quench evaluation ‐ TTC2014 Tsukuba 6
T‐mapping shows:heated zone along cavity axis is much shorter than along equator(due to magnetic field distribution?)
Time deviationOSTs close to quenched equator
show lower detection time (higher speed). Observed in all tests.Could be explained by heat propagation in Nb.5
5D.Sergatskov et al. ‐ Quench Dynamics in SRF Cavities ‐ SRF2013
Y.Tamashevich ‐ New insights into Second sound quench evaluation ‐ TTC2014 Tsukuba 7
Only in Direct view Only Hidden
Detectors in Line of Sight and in shadow
Even only OSTs in the ‘shadow’ could be used to determine the quench position
Y.Tamashevich ‐ New insights into Second sound quench evaluation ‐ TTC2014 Tsukuba 8
Quench position deviationEach combination of 3 OST leads to different quench positionThis deviation distribution is nicely fitted by normal distribution function
Y.Tamashevich ‐ New insights into Second sound quench evaluation ‐ TTC2014 Tsukuba 9
Comparing with T‐mapping results
Second Sound map T‐map
T‐mapping shows the quench point close to the spot defined by Second Sound test
OBACHTThis region on previous optical inspection*
*New EP was done before cold test. Not inspected yet
Y.Tamashevich ‐ New insights into Second sound quench evaluation ‐ TTC2014 Tsukuba 11
Defining the Second Sound velocitylinear fitting of all signals
calculated for every point of cavity surface
Lowest error
v = 19.63 m/sec (±0.17 m/s for 95%)
=284°, z=144 mmRMSEmin=0.37 m/sec Trilateration:
v = 20.1 m/sec(±5.7 m/s for 95%)
Conclusions
• Information of every OST can be used for evaluation of quench location (not only in line of sight)
• Significantly lower numbers of OST could be used (4‐6)• No problems with constrain quench position to the surface• Allows simulating of different effects of Second Sound propagation
Under development• Adding the effect of heat propagation in Nb to increase precision
This method allows to perform the SecondSound test of dressed cavitiesunder development
Acknowledgements:DESY FLA/ILC groupDESY MKS, MVS groups
Thank you!
Second Sound tests of other cavities
Temperature mapping